For the addition of the individual voltages of fuel cells and achieving a higher total voltage which this entails, it is known to connect several fuel cells electrically in series. Evidently then, for this, several fuel cells are connected together in a fuel cell system.
Usually for this, several fuel cells are arranged above one another and are pressed together by two end plates by way of screw connections (stack design). However, with regard to the geometry of the fuel cell system, a large constructional height and an unfavourable ratio of the edge length of the fuel cell system result on account of this design.
Since, for many applications, it is desirable to realise a fuel cell system with a significantly flatter geometry, there exists the need to connect the fuel cells in a fuel cell system in series in a plane. Here there are various ideas known from the state of the art:
The patent document DE 195 02 391 C1 and the PCT published application document WO 96/18217 disclose so-called “strip membrane fuel cells” with which the fuel cells are arranged next to one another and are connected to one another in series. The series connection is realised here in a manner such that a traverse conducting structure connects the cathode side of a fuel cell to the anode side of a further fuel cell and at the same time penetrates through the membrane contained in the fuel cells. With this, there exists the disadvantage that leakages may easily occur due to the passage of the transverse conductor through the membrane.
The U.S. Pat. No. 6,127,058 discloses a fuel cell system with which the fuel cells are arranged in a plane and are connected in series by way of outer-lying connecting lugs. With this solution, although the current path does not penetrate the membrane, the technical manufacturing expense is very active and prone to breakdown on account of the design, particularly with regard to the individual large-scale manufacture. Furthermore, it is considerably disadvantageous that at least two parts to be assembled individually as current dischargers are required for each cell.
In S. J. C Cleghorn et al.: “A printed circuit board approach to measuring current distribution in a fuel cell”, Journal of Applied Electrochemistry 28 (1998) 663-627, the idea of measuring the current distribution of a fuel cell by way of using a fuel cell whose current collector and gas distribution structure (flow field) on the anode side has been realised in a construction manner of a [printed] circuit board and in a segmented manner is described. The construction described here however is only suitable for locally resolved diagnosis purposes in the experimental field. Here too there is no series connection since for these diagnosis and measurement purposes (current, voltage, impedance spectroscopy) only individual cell segments are tapped.
It is the object of the present invention to specify a fuel cell system which has a low technical expense and may be manufactured economically in industrial large-scale manufacture, which is robust in its field of application and may be applied in a manner which is particularly technically simple, which has a flat geometry and which delivers an increased output voltage with respect to fuel cells contained in the fuel cell system. Furthermore, the disadvantages of the mentioned state of the art are to be avoided.
It is further the object of the invention to specify a method for manufacturing such a fuel cell system.
This object preferbly is achieved by the characterizing features of the present invention.